1. Field of the Invention
The invention relates to a method for forming bump electrodes on the surface of an electronic part such as a chip or a substrate.
2. Description of the Prior Art
In order to make an electronic part such as a chip or a substrate smaller and more compact, methods for forming bump electrodes on patterning electrodes on the surface of a chip or a substrate are well known. Hereinafter, conventional methods for forming bump electrodes will be illustrated.
FIGS. 8(a), (b), (c) show the conventional method for forming bump electrodes. In FIG. 8(a), solder balls 1 are accommodated in a vessel 2, a pick up head 3 is provided with a plurality of holes 4 on the lower face thereof for vacuum-attracting the solder balls 1. By up and down motions above the vessel 2 of the pick up head 3 sucked the air therein in the direction shown with the broken arrow by a suction device (not shown), the solder balls are vacuum attracted at the holes 4 and picked up. Then, the pick up head 3 moves above a vessel (not shown) stored with flux, and again moves down and up to attach the flux to the lower faces of the solder balls 1.
Then, the pick up head 3 moves above a chip 5, and again moves down and up and release the vacuum attraction state of the solder balls 1 so as to transfer the solder balls 1 onto patterning electrodes formed on the surface of the chip 5. FIG. 8(b) is a perspective view of the chip with transferred solder balls 1. Then, the chip 5 is sent to a heating furnace of reflow type (not shown) and heated so that the solder balls are melted. After that, the solder balls are cooled and solidified by the air of ordinary temperature and results in bump electrodes of hemisphere shape as shown in FIG. 8(c). The chip 5 fabricated in this way is generally called Flip chip. Methods for forming bump electrodes utilizing solder balls may be applied to electronic parts such as IC packages and substrates. Said solder balls are generally made from solder plates, but the method is complicated and results in the problem of cost up of electronic parts like chips 5 made by utilizing solder balls 1. Other problem is that, the size of bump electrode have to be changed according to the kind of chips or substrates though, changing the size of bumps is difficult in said conventional methods.